Fuel injection devices for operating an internal combustion engine have been known in general for many years. In a common rail injection system, fuel injection takes place in the respective combustion chamber of the internal combustion engine by means of injectors, in particular piezo injectors. Here, the quality of the combustion is dependent upon the pressure in the high pressure storage unit. In order to achieve as high a specific performance of the internal combustion engine as possible and at the same time low emissions of pollutants, the pressure of a high pressure storage unit must be controlled. When using a high pressure pump and a pressure storage unit for the fuel, injection pressures can reach between 1600 and 1800 bar.
Control of the pressure in the high pressure storage unit can be carried out in different ways. Depending on the embodiment of the injection system, this can be achieved with a pressure control valve in the high pressure region and a volume control valve on the low pressure side of the high pressure pump or just with a volume control valve on the low pressure side of the high pressure pump. Only the second case, i.e. pressure control with a volume control valve, is described in detail in the following. Control of the pressure in the high pressure storage unit takes place by controlling the volume flow in the low pressure region of the high pressure pump. This volume flow control is dependent both on system requirements which are determined by the quantity of fuel injected into the combustion chamber and also by the quantity of fuel which exits the injectors by switch leakage losses.
The volume flow control can thereby take place by means of gate valves. These are however not suitable for a volume flow control since they generally experience gap leakage losses via the pistons. These gap leakage losses are larger when the injection system is used in idling mode or in overrun conditions.
In the volume flow control a stop valve such as a ball which is pushed into a seat, completely cuts off the volume through-flow by means of a seat valve and thus prevents gap losses from occuring. In the seat valve, however, the pressure acting on the stop valve has an effect on the required supply of electric current to the valve. In this way, a change in pressure results in the shifting of a recorded valve characteristic curve. In the valve characteristic curve, the required supply of electric current to the valve is recorded dependent on the volume flow to be set.